Rattlesnake envenomation is not uncommon in the United States. Due to the widespread use of antivenom, few bites result in death; however, most bites do rise to severe hemorrhage and necrosis which often results in dysfunction or loss of the affected area. This proposal is directed towards understanding the mechanism of action of hemorrhagic toxins from rattlesnake venom by investigating the structure and substrate specificity of the hemorrhagic-proteolytic toxins. The amino acid sequences of hemorrhagic toxins isolated from Crotalus atrox venom will be determined in order to ascertain whether structural similarities exist among the toxins and also with other proteolytic enzymes. This information should give some indication as to what class of proteolytic enzymes these toxins belong. We will then proceed to determine what peptide bond specificities these toxins have for their proteolytic function. Peptide substrates with known sequences will be subjected to digestion by the toxins and the resultant fragments analyzed so that bond specificities can be assigned. These studies will allow us to rationally design synthetic peptides modified such that they may function as competitive inhibitors towards the toxins. The peptides will be synthesized via the solid-phase method and synthesis will involve such techniques as modification f amino acid side chains, backbone length variation, and residue substitutions to provide means for a competitive inhibition interaction with the toxins. The synthetic peptides will be assayed for their effectiveness as inhibitors using in vivo hemorrhagic assays and standard proteolysis assays. This research will hopefully lead to more effective methods of crotalid bite treatment such that local tissue damage may be avoided.